Hydraulic brakes as dealt with herein are today produced with a piston made from metal. The piston is slidably yet sealingly received in a cylinder bore provided in a calliper. The piston acts due to its movement on a brake pad which increases the friction between a brake disc and the brake pad. As the movement of the piston and pressure asserted on the brake pad from the piston are provided by the pressurised hydraulic fluid in the void below the piston in the cylinder in which the piston is arranged, a sealing must be provided between the skirt of the piston and the cylinder wall. Such a sealing is made from a flexible sealing, typically made from a polymeric material, arranged in a groove in the cylinder wall, which sealing fills the clearance provided between the piston skirt and the cylinder wall.
While this has proven to be a workable solution in systems where the piston is activated—that is moved by the hydraulic fluid relatively to the cylinder wall—on a regular basis in vehicle brakes, it has been found that in wind turbine applications, where the brake not necessarily is activated regularly, that there is a risk of the movement of the piston becomes hindered due to corrosion of the piston and the cylinder wall, as well as less effective during longer standstill.
Furthermore, the movement of the piston in the cylinder bore results in friction deteriorating the sealing, the piston itself and the cylinder bore. Such wear often results in leaks hampering the braking effect obtainable.
In addition, the known brake callipers require delicate machining such as grinding, polishing, honing etc. to obtain suitable friction characteristics and fitting between the calliper and piston.
An often devastating problem with the known callipers is that the piston may be wedged in the cylinder bore so that no movement of the piston—and thereby no brake effect—can be obtained.
Furthermore, the mass of the known callipers is often high due to the strength requirement and the metal compositions used for the parts which often are disadvantageous.
Hence, an improved brake calliper for a wind turbine application would be advantageous, and in particular a more efficient and/or reliable brake for a wind turbine would be advantageous.
It is a further object of the present invention to provide an alternative to the prior art.
In particular, it may be seen as an object of the present invention to provide a wind turbine 20 hydraulic brake calliper, a wind turbine hydraulic brake system and a wind turbine with a hydraulic brake calliper and/or system that solves the abovementioned problems of the prior art.